Valve unit for an electrostatic coating installation

ABSTRACT

The main needle valve of an electrostatic atomizer has an opto-electronic sensor device with optical waveguides whose faces are opposite a reflecting element of a component moveable with the valve needle for potential-free switch position interrogations.

SUMMARY

The main needle valve of an electrostatic atomizer has an opto-electronic sensor device with optical waveguides (20, 21) whose faces are opposite a reflecting element (12) of a component (10) moveable with the valve needle (1) for potential-free switch position interrogations.

DESCRIPTION

The invention concerns a valve unit according to the preamble of claim 1, especially for an atomizer under high voltage during operation for series coating of vehicle bodies, for example.

In known electrostatic rotary or air atomizers of this type (DE 4306800 A and Durr/Behr “EcoGun ESTA”), the paint line at the input to the atomization device is opened and closed with a paint needle valve, the so-called main needle valve, whose valve needle is pulled from the closed position against the force of a restoring spring into the open position by the piston of a pneumatic valve drive under control by the higher level program control system of the coating installation.

Feedback of at least one and preferably both switch positions of the main or paint needle valve is desirable for the higher level installation control. For example, in non-electrostatic air atomizers it was possible and common to generate the desired switch position signals with Hall sensors or inductive sensors mounted on the valve drive. These electric sensors, however, cannot be used in electrostatic atomizers that are under high voltage during operation. Although a switch position interrogation would also be important here, no practicable possibility has thus far been available for this.

Recording of the switch position of a valve needle for control of paint flow occurs, on the one hand, to monitor the switching function by feedback and, on the other hand, for valve control. By recording the time between the control signal of a valve needle and feedback of the switch position change in comparison with a stipulated reference value, deviations related to the operation (for example, by component wear) can be recognized and compensated in terms of process control. Because of this, especially in painting robots that operate with high painting speeds and frequent engagement/disengagement of valve needles, better constancy of the processes is possible.

There are also pneumatic sensors for interrogation of the switch position of valves, which, however, are too slow for the dynamic processes considered here.

The underlying task of the invention is therefore to provide a valve unit whose switch position even under high voltage can be interrogated as free of delay as possible.

This task is solved by the features of the patent claims.

With the invention, a potential-free and therefore switch position signaling also appropriate for electrostatic atomizers is made possible, for example, for main needle interrogation. The switch position of other valves situated in an electrostatic atomizer or in other components of a coating installation under high voltage can also be interrogated in the manner described here. The valve can also be a diaphragm valve.

The invention is further explained in the electrostatic rotary atomizer for direct charging of coating material shown in the drawing as an embodiment example. In the drawing,

FIG. 1 shows the rotary atomizer with the valve unit; and

FIG. 2 and FIG. 3 show two modified embodiments.

The atomizer depicted in FIG. 1 has the usual main needle valve with valve needle 1 for opening and closing of the paint channel 2 that discharges into the atomizer bell 4. The valve needle is moveable along its axis in the coaxial paint tube 3 containing paint channel 2. A pneumatic valve drive with a piston 6 is provided for valve operation, which piston is acted upon by compressed air for opening of the main needle valve at 7 and as a result of this pulls the valve needle 1 fastened to it against the force of a compression spring 8 engaging on its back sides rightward in the drawing in the direction facing away from the atomizer bell 4. The atomizer is known per se to this extent. The entire paint guide system of the atomizer can lie at a high voltage potential during operation on the order of, say, 100 kV.

A tappet or shaft element 10 that can be arranged coaxial with the valve needle 1, for example, within compression spring 8, is mounted on the piston 6 on its back side facing away from valve needle 1. The shaft element 10 according to the depiction expediently has on the periphery of its end part 11 facing away from piston 6 an optically reflecting surface element 12. The reflecting surface of element 12 can be flat and extend around the entire periphery, for example, of the square end part of the shaft (in cross section).

The end part 11 provided with the reflecting element 12 is shown in the drawing in the two switch positions of the main needle valve. They can be seen at 11, 12 in the (left) closed position, and in the valve open position at 11′, 12′ (right). The needle lift H between these two switch positions can be about 5 mm.

The shaft 10 is moveable in a recess 14 of the valve housing coaxial to the needle axis, into which a radially running opening 15 leads, i.e., transverse to the needle axis through the housing. A retaining and positioning element 17 for two optical waveguide units 20 and 21 fits in opening 15, the optical faces of which units are aligned with the inside wall of recess 14 at both sites at which the reflecting element 12, 12′ is situated in the two switch positions. The reflecting element therefore lies right against the face of optical waveguide unit 20 when the main needle valve is closed and opposite the face of unit 21 when the valve is opened. The mutual spacing of the center axes of units 20, 21 corresponds to the valve needle lift H. As a result, the two switch positions can be reported by light signals that are formed when light is fed from the outside through the corresponding optical waveguide unit, reflected by the element 11, 11′ and fed back through the same optical waveguide unit (or possibly another optical waveguide) to an optoelectronic sensor (not shown), which can be situated outside of the high voltage region.

Optical waveguide sensor systems appropriate for the described purpose are known per se and need no further description.

Instead of the depicted arrangement of the reflecting surface element 12 on various or all peripheral parts on the end of the shaft element 10, which permits arbitrary rotational positions of the shaft with reference to the optical waveguide 20, 21, one reflecting surface only on the peripheral part facing the optical waveguide is sufficient. The switch position interrogation can also occur on other sites of the valve needle itself or a component moveable with it.

In some instances, a single optical waveguide unit can also be sufficient for interrogation of only one of the two switch positions.

Instead of the radial arrangement of the optical waveguide in the depicted practical example, it is also possible to arrange an optical waveguide axially along the shaft element, whose switch position is recognized by differently intense reflection.

Another possibility of modification is arrangement of at least one opto-electronic light barrier, for example, on the shaft element 10 for potential-free interrogation of one or both switch positions. FIG. 2 shows an embodiment with two optical waveguides LWL1 and LWL2 arranged aligned with each other radially on opposite sides of the shaft element. In the depicted switch position, the waveguide LWL2 can guide light pulses sent from waveguide LWL1 to the optical electronic transducer, whereas in the other position of the shaft element end, the light barrier closes. In the embodiment according to FIG. 3, on the other hand, both switch positions can be actively interrogated, since here a hole 30 leading through the shaft element radially and positioned between two aligned optical waveguides LWL1, LWL2 and LWL1′, LWL2′ is present. According to another possibility (not shown), the main needle valve shown in the drawing can be modified so that at least one magnetically active sensor element is arranged on or in the moveable shaft element 10, for example, instead of the reflecting element 12 in FIG. 1 or the hole 30 in FIG. 3. In this modification at least one sensor element that exploits the magneto-optic Faraday effect or Kerr effect and that contains an optical polarization device with an analyzer serves as sensor device for interrogation of the switch position arranged on the moveable shaft element. The transmitter element can be a permanent magnet or also an element made of iron or another material with ferromagnetic properties with which the magnetic field of a magnetic element contained in the sensor element is variable. By approach of the transmitter element moving with the shaft element 10, the polarization direction of the light guided by the polarization device can be rotated in the sensor element to generate a light signal. An optical waveguide arrangement connected to the polarization device leads to a remote electronic device situated outside of the high voltage region to generate an electrical signal corresponding to the light signal. The sensor element can contain a reflector that guides the light coming from the polarization device back to the analyzer in which a refraction element (Faraday effect element) or a prism is situated between the polarization device and the reflector and a light guide for the light fed to the sensor element and the light guide for the light fed to the remote electronic device are connected to the polarization device. Such optical sensors are known per se and are commercially available. In the case described here, however, they have a special and surprising advantage in that they can operate without problem under high voltage. Depending on the expediency, one or two sensors, for example, can be arranged on the sites of the optical waveguides 20 and/or 21 in FIG. 1.

Especially when only one optical waveguide unit is arranged on the moveable shaft element 10 and the second optical waveguide 21 in FIG. 1 or the second unit with the optical waveguides LWL1′, LWL2′ in FIG. 3 are to be avoided, it can be expedient that two signal generation elements spaced from each other in the direction of movement be provided on the moveable shaft element 10, the first element of which triggers a binary signal of the sensor device, when the valve needle 1 is situated in one switch position, whereas the second signal generation element triggers a binary signal of the sensor device when the valve needle 1 is in its other switch position. According to FIGS. 1 and 3, the two signal generation elements can be formed by reflecting surfaces, between which a nonreflecting or slightly reflecting surface is situated, or through spaced light barrier openings. An embodiment with two permanent magnets or magnetically active transmitting elements at a spacing in shaft element 10 is also possible for the aforementioned Faraday effect or Kerr effect.

The binary signals triggered by the sensor in the two switch positions expediently have the same binary value. The binary signals are generated by the electronic sensor device, which is situated at a site removed from the valve outside of the high voltage region and is connected to the valve unit via the optical waveguide arrangement. When the shaft element 10 is displaced between its two positions, the sensor signal changes because of the region lying between the two signal generation elements initially into the opposite binary value before the first binary value is again generated on reaching the other valve position. By means of an electronic control device, it can be established whether, for example, after generation of a control signal for switching of the valve (and after disappearance of the first binary value), the first binary value is generated again as notification of the other valve position within a stipulated time. If this is not the case, a disturbance is present that is reported by an alarm signal. 

1. A valve unit for an electrostatic installation for series coating of workpieces, comprising a remote-controlled switchable valve whose moveable valve element is moveable between two switch positions and in one switch position releases a path for a medium flowing through the valve, whereas said valve is closed when said valve element is situated in its other switch position, wherein for interrogation of the switch position of said valve and for generation of a corresponding interrogation signal, an opto-electronic sensor device with at least one optical waveguide sensing movement of said valve element between at least two switch positions.
 2. The valve unit according to claim 1, where said moveable component has at least one optically reflecting surface opposite a sensor surface of said optical waveguide when said valve element is situated in the switch position to be reported.
 3. The valve unit according to claim 1, comprising one optoelectronic sensor device with at least one optical waveguide is provided for each of the switch positions.
 4. The valve unit according to claim 1, wherein said moveable valve element is the valve needle of a needle valve.
 5. The valve unit according to claim 4, wherein said moveable component is a shaft element mounted coaxial to valve needle on a piston of a pneumatic valve drive, said shaft element being moveable in a recess of a valve housing, into which a radial opening with respect to an axis of said valve needle leads for said optical waveguide.
 6. The valve unit according to claim 1, wherein said moveable valve element is connected to the diaphragm of a diaphragm valve.
 7. The valve unit according to claim 1, wherein said optical waveguides form at least one light barrier for said moveable component.
 8. The valve unit according to claim 1, wherein a magnetically active transmitter element is arranged on said moveable component, that a sensor element is provided that contains an optical polarization device, that by approach of the transmitter element the polarization of the light guided through said polarization device is varied in said sensor element magneto-optically to generate a light signal, and that an optical waveguide arrangement is connected to said polarization device, which leads to a remote electronic device to generate an electric signal corresponding to said light signal.
 9. The valve unit according to claim 8, wherein said sensor element contains a reflector that guides the light coming from said polarization device back to an analyzer of said polarization device, in which a refraction element that rotates the direction of polarization is situated between said polarization device and said reflector and that a light guide for the light fed to the sensor element and said light guide for the light fed to said remote electronic device are connected to said polarization device.
 10. Said valve unit according to claim 9 wherein said moveable component includes two signal generation elements spaced from each other in the direction of displacement, said first element of which triggers a binary signal of said sensor device when the valve element is situated in one switch position, whereas said second signal generation element triggers the binary signal of said sensor device with the valve element situated in its other switch position.
 11. The valve unit according to claim 10, wherein said two signal generation elements of said moveable component are formed from optically reflecting surfaces.
 12. The valve unit according to claim 10, wherein said two signal generation elements are formed by light barrier openings.
 13. The valve unit according to claim 10, wherein said two binary signals have the same binary value and that said sensor signal of the sensor device is switched to the opposite binary value when said moveable component is shifted between its two positions.
 14. The valve unit according to claim 10, comprising an electronic control device with which it is established that the binary signal appears within a stipulated time after generation of the control signal for switching of said valve and that otherwise an alarm signal is generated. 